Exploration of the mechanisms by which nutrient intake modifies gene expression may reveal the mean by which dietary factors can alter susceptibility to cancer. This work will examine the expression and regulation of the gene for the liver selenoenzyme glutathione peroxidase (GSH:H2O2 oxidoreductase, EC 1.11.19) (GSH-Px). Dependence of that regulation on dietary intake of selenium (Se) will be determined. This requires the isolation and structural and organizational characterization of the rat liver GSH-Px gene. Dependence of transcriptional or translational regulation on diet will be examined by comparing run-off transcripts, accumulation and stability of GSH-Px mRNA, and accumulation and stability of anti-GSH-Px antibody-reactive protein from livers of rats fed Se-deficient or Se-adequate diets. These experiments will show which reactions in the expression of the GSH-Px gene are most sensitive to dietary Se intake. To examine one mechanism by which dietary SE intake may regulate expression of the GSH-Px gene, electrophoretic mobility shift (EMS) assays and methylation interference assays will be done. These experiments will demonstrate binding of trans acting factors (proteins) to sequences in the flanking regions of the GSH-Px gene. Assays performed with lever nuclear extracts from se-adequate and Se-deficient animals will demonstrate the dependence of potential regulatory proteins on dietary Se intake. The use of nuclear extracts in these assays from livers of rats injected with 75 Se will show whether or not selenoproteins themselves, or Se-binding proteins, inducible by dietary Se intake, play a role in the regulation of the GSH-Px gene.